linux-kernel - Re: [PATCH -next v2 6/7] ext4: simply the mapping query logic in ext4_iomap

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Message-ID: <65ffdc21-1f94-428c-be06-f81c87f019bc@huawei.com>
Date: Wed, 31 Dec 2025 15:46:14 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Zhang Yi <yi.zhang@...weicloud.com>, <linux-ext4@...r.kernel.org>
CC: <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
	<ojaswin@...ux.ibm.com>, <ritesh.list@...il.com>, <yi.zhang@...wei.com>,
	<yizhang089@...il.com>, <yangerkun@...wei.com>, <yukuai@...as.com>
Subject: Re: [PATCH -next v2 6/7] ext4: simply the mapping query logic in
 ext4_iomap_begin()

On 2025-12-23 09:18, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
>
> In the write path mapping check of ext4_iomap_begin(), the return value
> 'ret' should never greater than orig_mlen. If 'ret' equals 'orig_mlen',
> it can be returned directly without checking IOMAP_ATOMIC.
>
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> Reviewed-by: Jan Kara <jack@...e.cz>

Looks good. Feel free to add:

Reviewed-by: Baokun Li <libaokun1@...wei.com>

> ---
>  fs/ext4/inode.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index b84a2a10dfb8..67fe7d0f47e3 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3816,17 +3816,19 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  		if (offset + length <= i_size_read(inode)) {
>  			ret = ext4_map_blocks(NULL, inode, &map, 0);
>  			/*
> -			 * For atomic writes the entire requested length should
> -			 * be mapped. For DAX we convert extents to initialized
> -			 * ones before copying the data, otherwise we do it
> -			 * after I/O so there's no need to call into
> -			 * ext4_iomap_alloc().
> +			 * For DAX we convert extents to initialized ones before
> +			 * copying the data, otherwise we do it after I/O so
> +			 * there's no need to call into ext4_iomap_alloc().
>  			 */
>  			if ((map.m_flags & EXT4_MAP_MAPPED) ||
>  			    (!(flags & IOMAP_DAX) &&
>  			     (map.m_flags & EXT4_MAP_UNWRITTEN))) {
> -				if ((!(flags & IOMAP_ATOMIC) && ret > 0) ||
> -				   (flags & IOMAP_ATOMIC && ret >= orig_mlen))
> +				/*
> +				 * For atomic writes the entire requested
> +				 * length should be mapped.
> +				 */
> +				if (ret == orig_mlen ||
> +				    (!(flags & IOMAP_ATOMIC) && ret > 0))
>  					goto out;
>  			}
>  			map.m_len = orig_mlen;